Biological Treatment of Spent
Vegetable Tannins
CLINTON E. PARKER, Assistant Professor
Civil Engineering Department
University of Virginia
Charlottesville, Virginia
INTRODUCTION
During the summer of 1966 a wastewater survey and a bench scale pilot plant
study was sponsored by Virginia Oak Tannery, Inc. (VOTAN) in Luray, Virginia.
This waste study and pilot plant, and the results of a study at the University of
Cincinnati by Lin (1) were the basis for this investigation.
The purpose of this study was to evaluate and derive data for biological treatment of spent vegetable tannins blended with other tannery wastewater streams,
except lime and unhairing wastewater. The major effort in this study was to evaluate
the characteristics of a lagoon system in treating these wastes by loading the system
and observing it as conditions went from aerobic to anaerobic-aerobic and to evaluate
the effectiveness of the system in meeting the need for a low cost treatment method
capable of producing an effluent that meets pollution abatement standards. In
addition to the lagoon system, to further describe the spent tannins, a laboratory
completely mixed reactor was used to derive growth kinetic parameters.
Construction of a demonstration lagoon system at VOTAN was completed in
1968. Initially, spent tannins were blended with batepool and soak wastewater,
however, later in the study only spent tannins and batepool wastewater were blended
and fed the lagoon system. During the study, aeration was held constant and flow
(proportioned according to waste stream flows in the tannery) was varied between 15
gpm and 127 gpm.
This work was divided primarily into two areas: 1) a field demonstration
lagoon, and 2) the study of aerobic treatment of spent tannins in a completely mixed
laboratory reactor.
TANNERY WASTEWATERS
The conversion of animal hides, primarily cattle, into leather is generally comprised of ten separate physiochemical or biological processes (2,3). The tanning step
is the actual conversion of the fibers in the hide to leather. In present practice, two
primary methods of tanning are vegetable tanning and chrome tanning. For vegetable
tanning an aqueous extraction of certain forms of plant life is used as the tan
solution. The hides are emersed in a weak extraction and moved through an increase
in concentration, ranging from 0.3 to 6.0 per cent tanning extract. Preliminary
tanning is in rocker vats and takes about three weeks. This is followed by tanning in
layer vats with a 6.0 per cent tanning extract for another three weeks. Although tan
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